Interval counters are commonly used as event counters for measuring the occurrence of external events. Interval counters are commonly used in electronic circuitry for measuring the receipt of sequential input signals. The input signals may be produced by a wide variety of external electronic circuitry, such as circuitry used to detect the rotation of a spur gear. For example, an interval counter may be used as a missing pulse detector in order to detect the position of the spur gear by responding to a missing tooth on the gear. In the case of a spur gear, each gear tooth passing in front of a sensor creates an event and a missing tooth results in a break in the regular sequence of events. An interval counter is a general purpose device which may be used in order to accomplish a wide variety of tasks which require the monitoring of external events.
An analogous device to a retriggerable interval counter is a retriggerable "one-shot" or monostable multivibrator. A retriggerable "one-shot" is a digital integrated circuit which is used in order to produce an output interval signal each time that it is triggered. The "one-shot" will reset itself to produce a second interval signal if a second trigger is received after a first trigger. That is, the "one-shot" is retriggerable so that it will produce an output interval signal even through it has been previously triggered.
Because of the advent of the demand for miniaturized equipment that allows computer processor control over the detection of external events, prior interval counter circuitry has been inadequate to provide the needed performance.